CVE-2023-20168 in NX-OS
Summary
by MITRE • 08/23/2023
A vulnerability in TACACS+ and RADIUS remote authentication for Cisco NX-OS Software could allow an unauthenticated, local attacker to cause an affected device to unexpectedly reload. This vulnerability is due to incorrect input validation when processing an authentication attempt if the directed request option is enabled for TACACS+ or RADIUS. An attacker could exploit this vulnerability by entering a crafted string at the login prompt of an affected device. A successful exploit could allow the attacker to cause the affected device to unexpectedly reload, resulting in a denial of service (DoS) condition.
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Analysis
by VulDB Data Team • 09/16/2023
This vulnerability exists within Cisco NX-OS Software's implementation of TACACS+ and RADIUS remote authentication protocols, representing a critical security flaw that undermines the reliability of network device authentication systems. The issue specifically manifests when the directed request option is enabled for either TACACS+ or RADIUS authentication mechanisms, creating a condition where malformed input can trigger system instability. The vulnerability stems from insufficient input validation procedures that fail to properly sanitize or verify authentication requests before processing them, allowing maliciously crafted strings to bypass normal authentication flow and potentially disrupt system operations.
The technical exploitation of this vulnerability occurs through a carefully crafted string input entered at the login prompt of affected Cisco NX-OS devices, which triggers an unexpected system reload condition. This flaw operates at the authentication processing layer where the software fails to validate input parameters against expected formats and lengths, creating a path for malformed data to cause system crashes. The directed request option, when enabled, provides additional attack surface by allowing specific authentication parameters to be processed in ways that do not properly account for edge cases in input handling. This type of vulnerability aligns with CWE-129, Input Validation, and CWE-248, Uncaught Exception, as it demonstrates both insufficient validation of input parameters and improper exception handling during authentication processing.
The operational impact of this vulnerability extends beyond simple denial of service conditions, as it represents a potential vector for more sophisticated attacks targeting network infrastructure reliability. When an affected device experiences unexpected reloads, it creates temporary service disruption for network administrators and users who depend on those devices for authentication services. The vulnerability affects network security infrastructure by potentially creating windows of opportunity for attackers to disrupt authentication services or cause cascading failures in network operations. This type of DoS condition directly impacts the availability component of the CIA triad, as it prevents legitimate users from accessing network resources through authentication mechanisms.
Organizations should implement immediate mitigations including disabling the directed request option for TACACS+ and RADIUS authentication when not strictly required, applying available Cisco security patches, and implementing network segmentation to limit potential attack vectors. Network administrators should also monitor authentication logs for unusual patterns that might indicate exploitation attempts and establish robust incident response procedures for handling unexpected device reloads. The vulnerability demonstrates the importance of proper input validation in authentication systems and aligns with ATT&CK technique T1110.003, Password Guessing, as it represents an authentication bypass or disruption mechanism that could be leveraged in broader attack campaigns. Security teams should also consider implementing additional monitoring for authentication service availability and establish baseline performance metrics to quickly detect anomalous reload patterns that might indicate exploitation attempts.